Considering how lava rock or clay aggregate was originally made you can sterilize them without harming the medium. I once threw my lava rocks on top of a couple of sheets of aluminum foil on my gas grill. After 10 minutes I was pretty sure there were no parasites or anything else living on those rocks. Though I did not try it I was also considering using a propane torch with a fan nozzle on the rocks.

All you really have to do is boil the medium to kill the pathogens.

I have used expanded clay rocks for years and sterilize the used ones every two weeks in boiling water.

It's also good to use a soultion to remove mineral deposits left by nutrients on all stuff in contact with nutrients, including grow rocks. I use clearex every two weeks as well.

mix a little bleach with a little hydrogen peroxide and a bunch of water.

rinse thoroughly

i dont bother sterilzing anything anymore. heck i dont even clean the stuff between grows.

if you're getting deposits on the surface its because your tds/ec is too high.

H2O2 and CL will react with each other when mixed.

Cl2 + H2O HOCl + H+ + Cl-
Cl2 + H2O2 ----> O2 + 2HCl

H2O2 alone would be more effective. I think.

I have run into trouble not sterilizing.
Now I broil lava rocks in the oven.

My problem was that buckets full of lava went outside to dry on black plastic. I guess something that was wating the roots came back inside, as I got root rot for the forst time ever.

If you want to just replant, I have read of many growers watering the medium with and enzyme product that helps to digest the roots into matter the plants can take up.

Although I have read exellent reports in peat based mixes and perlite/vermiculite, it is sold at hobby hydro stores, not at commercial hydro stores.

Does this mean it is ineffective, or too expensive to meet industrial efficiency standards? I don't know, but it's not cheap.

cG

Cavemangardener, I wonder if part of the problem with the peat/perlite or Vermiculite mixes at commercial stores is that it is not a money making product rather than an industry standard. It is very cost effective product at some of the large hardware stores, so commercial hydro stores probably can not compete with their low prices. An exception is the Perlite. The Perlite I have seen sold at chain hardware stores is not of high quality. The higher grades I have seen are at stores that cater to professional growers. Another consideration is a less expensive pump may oftentimes be used with a media system, which might affect sales of the higher priced pumps.
The peat/perlite/vermiculite systems can take more work and can be messy to handle. They are, however, cheaper to set up to run, & the media can be recycled. They can require less powerful pumps, which is a money saver consideration during these higher fuel priced times.
If I were selling commercially, I would want to sell more money making products, such as ready made systems or media with a higher markup. This is just my opinion.

Dear penjingguy,
I do not go for fancy mediums, but use coarse sand with the fines shaken out with a sieve. I do not even sterilize the medium, but when it gets too dirty, I just churn it up in a small concrete mixer (maybe about every three years), and give it a good wash.
If you are worried about pathogens, just immerse the medium in Sodium Hypochlorite solution, which is a popular chlorine bleach. Just watch where you dispose of the drainings from the bleach and the subsequent washings. If you find the washing too much of a chore, you could use some Sodium Thiosulphate (photographic hypo) to kill off the chlorine.
Please have a look at my web site from Australia. It will tell you just about everything you want to know about hydroponics.
Jimr007
Australia.

Here is a link that might be useful: Simple Sand Hydroponics